This invention relates to a method of producing a polishing agent comprised of mother particles and very fine abrading particles, and in particular such a polishing agent comprised of mother particles on the surfaces of which very fine abrading particles are supported, as well as a method of polishing by using such a polishing agent.
Cloths of various kinds with free abrading particles are recently being used for the fine finishing in the production of high-tech electronic devices such as semiconductor substrates and magnetic disc substrates. In such a process, elastic cloths such as woven cloths, unwoven cloths and foamed substances are used for producing mirror surfaces. About 30 years ago, it was mostly woven cloths that were being used, but since the woven texture had adverse effects on the roughness and unevenness, they have gradually ceased to be used and unwoven cloths have come to be used mostly. Since unwoven cloths have unevenness in the density, however, it has been pointed that they also have adverse effects in the fine-scale unevenness. Thus, the use of foamed substances are now beginning to increase.
Recently, there is an increasing demand for processing with high precision in shape, and harder polishing cloths are coming to be favored. There are problems, however, with the use of a hard cloth such as the difficulty in achieving required roughness and the tendency to produce scratches. In view of such problems, there has also been a proposal to use a double-layered polishing cloth with a hard resin layer and a soft resin layer superposed one over the other.
Such prior art polishing agents and methods have many problems. Firstly, for example, the surface roughness of prior art polishing cloths becomes quickly diminished, and both scraped materials and the polishing materials become accumulated with the time of use such that the polishing efficiency is adversely affected. For this reason, the common practice is to use a diamond grinder to rework the cloth surface, which is a process referred to as the “conditioning”. This process tends to shorten the useful lifetime of the polishing cloth, and there is the problem of abrading particles dropping off from the diamond grinder and scratching the target surface being polished.
Secondly, since polishing cloths have a thickness of about 2-3 mm, their elastic deformation is relatively large and they sometimes come into a direct contact themselves with the target surface, thereby increasing the frictional resistance and hence also the power consumption by the polishing machine.
Recently, furthermore, it is sometimes required to polish a surface with a large diameter and accordingly larger polishing machines are coming to be used. In order to be used on such a larger polishing machine, the size of polishing cloths is also increasing. It takes the skill of a highly experienced worker to attach a large polishing cloth uniformly over the plate of a polishing machine.